1. Field of the Invention
The present invention generally relates to a measurement device and, more particularly, to a measurement device for measuring the gray-to-gray response time of a liquid crystal display (LCD).
2. Description of the Prior Art
For a liquid crystal display (LCD), the response time indicates the transition from a frame to another as the alignment of liquid crystal molecules changes. The response time affects the LCD video quality for motion pictures, especially for pictures in which objects are moving at a high speed. If the response time is slow, it is easy that image blur occurs. Typically, the response time is measured in milliseconds (ms, 1/100 second) to indicate the transition from a full black/white frame to a full white/black frame, i.e., the black-and-white transition. However, in practical uses, a frame seldom changes from black/white to full white/black. Instead, the frequency of gray-to-gray transitions is typically far greater than black-and-white transitions.
The gray-to-gray response time is defined by choosing two gray levels G1 and G2, wherein G1<G2. The rise time (Tr) is referred to as the transition time wherein the luminance rises from 10% to 90% during the G1-to-G2 transition, and the fall time (Tf) is referred to as the transition time wherein the luminance falls from 90% to 10% during the G2-to-G1 transition. The gray-to-gray response time for transition between G1 and G2 is the sum of the rise time and the fall time, i.e., Tr+Tf.
Since the gray-to-gray response time is measured using tested pictures with different gray levels G1 and G2 to be switched based on the same time interval. The luminance at the center of the display is measured by a measurement device so as to analyze the response time during the transition. Therefore, in the minimal range of optical variation, interference due to noise often leads to inaccuracy in gray-to-gray response time measurement. However, it is crucial to precisely measure the gray-to-gray response time because the image quality of the LCD significantly relies on the gray-to-gray response time. Thus, considering the follow-up image processing, it is very helpful to obtain accurate data of the gray-to-gray response time.